Me holding homemade fertilizer made from coffee grounds and crushed eggshells for the soil of my houseplants

Fertilize Indoor Plants Naturally With Homemade Fertilizers!

A lot of indoor gardeners aren’t aware of which household by-products can be used as homemade fertilizer. Without knowing, which common household products and by-products can be used as natural fertilizers, many indoor gardeners solely rely on store-bought products. That’s exactly why I created this list for you!

To fertilize indoor plants naturally, you can use Epsom salt, used aquarium water, banana peels, corn gluten meal, smashed eggshells, gelatin powder, molasses, leftover cooking water, coffee grounds, fireplace ashes, used green tea bags, and trimmed hair as homemade fertilizers.

I made a point to include a few unconventional options you may not have heard of before. Each homemade fertilizer works in a natural way to nourish your houseplants. I’ll explain more ahead, so keep reading!  

12 Ways to Fertilize Your Plants Naturally 

1. Epsom Salt

Epsom salt, also known as magnesium sulfate, is not the traditional table salt you have in your pantry right now. 

Rather, it’s a water-soluble, crystalline solid that breaks down when wet into its base ingredients, sulfate and magnesium.

So what does Epsom salt do for indoor plants? Well, if your houseplants suffer from a magnesium deficiency, Epsom salt can cure what’s ailing ‘em. 

You can usually tell that the issue is a magnesium deficiency specifically because the leaves of your houseplant will turn yellow while the veins remain green.

When it comes to using Epsom Salt on plants, don’t merely sprinkle Epsom salt on the top layer of the soil, as it’s still salt, and a lot of plants are sensitive to how much salt they receive. 

As far as how much to use, I’d recommend filling a gallon of water and diluting a tablespoon of Epsom salt in it before applying it to your plants.

Save this water/Epsom salt mix and either mist the plant with it or use it in lieu of pure water once per month. 

It’s tomatoes, peppers, and even roses that benefit from the sulfate and magnesium in Epsom Salt.

2. Used Aquarium Water

Do you have an aquarium full of fish? If so, then you probably dump the water straight outside when it’s time to change the tank, right?

Well, that’s a major missed opportunity!

Although it isn’t good for your fish to linger in dirty water for too long, there’s a lot of stuff in the water that your houseplants would love.

I’m talking about trace nutrients, nitrogen, phosphorus, potassium, and even helpful bacteria. 

If these ingredients sound familiar, it’s because they’re usually what’s in those commercial fertilizer bags you lug all over the garden supply store. You’re just omitting the questionably long chemical ingredients.

Okay, but is used aquarium water really the healthiest thing for your plants?

There’s nothing wrong with using old aquarium water as fertilizer unless you’re growing edible plants. Then you probably don’t want to douse your houseplants in used aquarium water since you’ll someday eat what your plant produces.

For ornamental and non-edible plants, it’s a-okay!

If you’re still a little concerned, you can always dilute the aquarium water with pure water, but keep in mind your plants won’t receive the same dose of nutrients that they would otherwise.

This is also assuming that the dirty aquarium water is just the regular levels of dirty and not filthy. You also shouldn’t use aquarium water if it’s from a saltwater tank.

To repurpose used aquarium water as fertilizer, all you have to do is replenish your plants with this water rather than pure water. 

Do this every few days as needed for several weeks until the aquarium water is gone. Be sure to still use pure water in between.    

3. Leftover Banana Peels

Bananas are great for us to eat, as this creamy fruit is an excellent source of potassium. 

Used banana peel sitting on the table before being used in a homemade natural fertilizer recipe

While you may sometimes add the peels to your compost pile, used banana peels have another purpose: Homemade plant fertilizer!

It’s not only bananas themselves that contain potassium but their peels as well. The peels might have over 40 percent potassium, so if you have a potassium-loving plant or two in your indoor garden, you know what to do.

Potassium is useful in helping houseplants ward off disease, and it leads to healthier stem growth as well.

Of course, banana peels have more than simply potassium. They also contain manganese that may help in photosynthesis as well as calcium for stopping blossom end rot.

You have three methods for using banana peels as fertilizer, so let’s go over them now.

The first is to make banana peel tea. Here are the steps.

  1. Transfer the banana peels to a bowl or jar and then pour in water. 
  2. Wait several days but ideally two weeks, as the longer the peels steep, the more nutrients can be extracted.
  3. Pour the banana water into your houseplant’s pot.
  4. Dry out the banana peel and add it to your compost pile.

You can also dry the banana peel out and then use it as fertilizer thusly.

  1. Cut the banana peel into pieces, then let them sit in the sunlight in a strainer for several days.
  2. Alternatively, if it’s not a sunny day, you can turn on your oven to low and let the peels roast for a couple of hours.
  3. Once the peels are adequately dried, insert the peels deep into your plant’s soil and moisten the soil.
  4. Now, whenever the peels get wet, they gradually release potassium, manganese, and calcium.

You can also simply cut the banana peels and use them as a more direct form of fertilizer. Let’s go over the steps.

  1. Cut the banana peels into pieces measuring about an inch apiece.
  2. Insert the banana peel pieces into the soil several inches deep. 
  3. Allow the banana peel to release nutrients over time. 

4. Corn Gluten Meal

A type of corn byproduct, corn gluten meal is a corn protein endosperm with glutelin and zein. It’s mostly used as animal feed and doesn’t have true gluten.

If you have some handy, corn gluten meal is highly beneficial for indoor plants. 

For one, it’s full of nitrogen, so if your houseplant has a deficiency or just needs more nitrogen, you can use the meal instead of commercial fertilizer.

More so, corn gluten meal is a natural weed preventer that comes in handy for indoor and outdoor gardens alike. 

You don’t have to worry about corn gluten meal harming your plants, unlike traditional fertilizers, and it’s really easy to use, too. Just sprinkle some of the meal on the surface of the soil.

Keep in mind that some weeds are unaffected by corn gluten meal, including quackgrass, dandelions, crabgrass, pigweed, purslane, and foxtail. 

5. Smashed Eggshells

Similar to not throwing away banana peels if you want to fertilize indoor plants naturally, I’d suggest holding onto your used eggshells as well.

smashed up used eggshells on the table before adding them to my potting soil

It’s okay if you don’t crack the shells with the precision you see on cooking shows, as you need to shatter the shells anyway.

So why eggshells for houseplants? That’s easy! Eggshells contain calcium carbonate which can improve root strength and encourage a plant to grow strong and quickly.

There are more reasons still to love eggshells. The calcium can prevent blossom end rot and reduce high soil pH. 

To crush eggshells, I’d recommend a mortar and pestle or a coffee grinder, not doing it by hand. You could cut your hands that way!

You can then take the eggshell powder and pour it straight into the houseplant’s soil. 

6. Gelatin Powder

Check your shelves, as you might have gelatin powder handy right now. If so, then congratulations, you’ve got a natural plant fertilizer.

Gelatin powder is simply gelatin that’s first dried out and then broken down one grain at a time. It has the benefit of providing nitrogen to houseplants.

Even better is that gelatin powder is a time-released natural fertilizer so a little goes a long way. 

To make it into a fertilizer, you need pure gelatin.

Make sure it’s the unflavored stuff as well. While you might appreciate flavored gelatin, your plants do not. 

Steep the unflavored gelatin powder in hot water, stirring until it’s seemingly dissolved. 

Allow the water to cool down, pour some into a gardening can or spray bottle, and then apply directly to the soil.

Do keep in mind that gelatin powder is only a good source of nitrogen and not potassium or phosphorus, so you’ll have to use other natural fertilizers for those macronutrients. 

7. Molasses

Now here’s one I’m sure you’re thinking is quite strange, am I right?

Molasses comes in handy when baking gingerbread cookies around the holidays, but it’s also useful for fortifying houseplants. 

How so? Well, molasses naturally contains micronutrients as well as high levels of potassium, iron, magnesium, and calcium. 

Magnesium helps plants metabolize chlorophyll, potassium regulates water levels and enzyme activity, iron produces enzymes, and calcium assists in root absorption. 

Even the sugar in molasses is okay, as microorganisms in your plant’s soil can feed on those sugars. 

It’s not as simple as opening that jar of molasses you have and watching the dark-colored, viscous liquid seep into your plant’s soil. Please do not do that.

First of all, not every type of molasses is right for the job. You should use unsulfured blackstrap molasses only. 

The sulfur that’s in other types of molasses can kill any microorganisms or microbes in your houseplant’s soil.

You can dilute molasses with water, transfer it into a spray bottle, and then mist your indoor plant’s leaves. The readily available nutrients as well as the sugar are all absorbed at a rapid rate. 

8. Leftover Cooking Water

Once you use aquarium water as a form of natural houseplant fertilizer, the thought of doing the same with leftover cooking water shouldn’t be so odd. 

After steaming vegetables, boiling eggs, or boiling pasta, keep that water in the pot instead of pouring it through a strainer and down your sink.   

When you boil pasta, veggies like potatoes, and eggs, it’s not merely that you’re softening these foods. The boiling process also releases calcium, nitrogen, phosphorous, and micronutrients into the water. 

These nutrients, as you know by now, can sustain houseplants without the chemical residue of commercial fertilizers. 

Give the water time to cool down after boiling and then pour it into a jug or another container to keep it. 

The next time you need to water your plants, use the cooking water instead. 

You can alternate between pure water and cooking water to ensure your plants receive the macro and micronutrients they need.

Ultimately, you can get choosy about which foods you’re boiling to ensure an even mix of nutrients. To start though, pasta water or veggie water is more than fine. 

9. Coffee Grounds

You may recall in my previous post Do Indoor Plants Like Coffee Grounds? that some houseplants love coffee grounds! 

Do Houseplants REALLY Like Coffee Indoor plant with liquid coffee and coffee grounds

Additionally, coffee grounds might lure in earthworms to the soil and benefit the microorganisms that already call your plant’s soil home. 

The grounds come in handy as more than a fertilizer but as a compost ingredient, a pesticide, and a mulch as well.

As a fertilizer, coffee grounds are rich in nitrogen but also don’t slack off when it comes to their potassium and phosphorus content as well as micronutrient content. 

Some plants react better to coffee grounds than others. I’d recommend using grounds for African violets, miniature roses, golden pothos, philodendrons, Christmas cacti, jade plants, cyclamen, and peace lilies.

Please only use coffee grounds from black coffee. If you’ve stirred in additives like milk, cream, or sugar, then the coffee grounds are tainted. 

Applying coffee grounds as a fertilizer would then only lead to fungal disease, fungus gnats, and possibly mold as well. 

Once you’ve got black coffee grounds ready to go, gently sprinkle them atop the soil. Don’t bury the soil in coffee grounds, as less is certainly more here.

Here’s something to keep in mind: coffee grounds are considered a natural form of slow-release fertilizer. You should not expect instant results when using the grounds.  

10. Outdoor or Fireplace Ashes

In the autumn, nothing is better than a fire pit, just as throughout the winter, the roaring fire from your fireplace is one of the most welcome sights.

What do you normally do with your ashes when you’re done? Dispose of them?

Well, why do that when you can use the ashes as plant fertilizer instead?

Wood ash especially can increase soil pH and boost the soil’s fertility, providing a healthier setting in which your plant can grow. 

The ash contains about 20 percent calcium on average as well as potassium at a rate of about five percent. Phosphorus and magnesium are in wood ash too at a rate of about two percent each, according to the University of Wisconsin-Madison

Don’t forget the micronutrients such as boron, zinc, manganese, aluminum, and iron, which wood ash is rich in.

Since ash raises soil alkalinity, that does disqualify it as a natural fertilizer contender for houseplant species outside of rhododendrons, azaleas, blueberries, and other acid-loving plants.

The cleaner the wood ash is, the more beneficial for your indoor garden. Any ash that’s the byproduct of burning garbage, plastic, waste oil, or treated wood should not be used.

The same goes for wood ash from trees grown around toxic contamination and/or industrial sites. 

Once you have wood ash, sift it, as the stuff may contain embers or charcoal. 

Like you would when using coffee grounds as a natural plant fertilizer, the key here is to use a light hand. Less ash is better than more. 

11. Used Green Tea Bags

As I’m sure you’re getting used to by now, holding onto your cooking byproducts when you’re done with them is a wise idea.

Teabags in general are advantageous to houseplants, but I recommend green tea bags specifically. 

Why is that? Green tea has plenty of nitrogen as well as lots of phosphorous and potassium. 

The teabags will add moisture to your plant’s soil, augment drainage, and benefit the soil structure.

Oh, and green tea bags can also encourage earthworms in the soil. 

To use green tea bags as fertilizer, you can insert the bags manually into your houseplant’s soil. The teabags will naturally decompose and release nutrients into the soil when they do!

12. Trimmed or Excess Pet and Human Hair 

Listen, I know how weird this last one sounds. That doesn’t mean it’s not effective!

Oregon State University notes that human hair has high amounts of carbon (51 percent), oxygen (21 percent), nitrogen (17 percent), hydrogen (six percent), and sulfur (five percent).

Plants thrive on these macro and micronutrients, so offering up your own hair as a form of plant fertilizer is warranted.

I’m not saying you have to cut your hair right now. The next time you do an at-home trim though, keep some of the hair. 

Pet hair should have similar properties, so if you have a heavily-shedding dog or cat, don’t throw their spare hair away! It’s a goldmine of nutrients.

You can always grind hair down and incorporate it into the soil or growing medium following a 3:1 ratio with more soil than hair. 

Another option is to incorporate the hair into the soil.

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